Spanner migration tool is a stand-alone open source tool for Cloud Spanner evaluation and migration, using data from an existing PostgreSQL, MySQL, SQL Server or Oracle database. The tool ingests schema and data from either a pg_dump/mysqldump file or directly from the source database, and supports both schema and data migration. For schema migration, Spanner migration tool automatically builds a Spanner schema from the schema of the source database. This schema can be customized using the Spanner migration tool schema assistant and a new Spanner database is created using the Spanner schema built.
Installation instructions for Spanner migration tool are available here.
Detailed documentation on how to use spanner-migration-tool is available at: https://googlecloudplatform.github.io/spanner-migration-tool